This application is related to: U.S. patent application Ser. No. 08/007,849, filed Jan. 22, 1993 (still pending), entitled "Reusing Device Driver Stubs to Support Access to Removable Computer Cards", which is hereby incorporated fully by reference.
1. Field of the Invention
The present invention pertains to the field of computer systems. Specifically, the present invention relates to computer systems supporting an interface to removable system resources and the control of device drivers related thereto.
2. Art Background
It is becoming increasingly important to design and build computer systems that can be dynamically configured without powering down the computer system or requiring the operating system program logic to be reset or bootstrap initialized. Dynamic configuration includes the ability to add or remove system resources or special feature capabilities while a computer system is operating. These system resources and special features include expansion memory boards, parallel or serial input/output (I/O) ports, read only memory (ROM) or flash memory expansion boards, computer network interface cards, modem cards, smart cards, or other removable system resources or special feature mechanisms.
Such removable system resources and special features are often implemented in the prior art using removable electronic feature cards adhering to the Personal Computer Memory Card International Association (PCMCIA), Sunnyvale, Calif., Release 2.0 standard. These PCMCIA feature cards generally comprise electronic microcircuits within a thin housing including a detachable multiple conductor interface with which the feature card may be removably inserted into a slot in a computer housing. Once inserted, a feature card is accessible to and used by the processor in the computer system. The use of feature cards allows a computer user to select specific features or resources from a variety of feature cards offered by a computer vendor. In this way, the computer user achieves the desired level of functionality without being required to purchase unnecessary resources or computer system capabilities. The overall cost of the computer system for a specific application is thereby optimized. The use of removable feature cards is particularly significant for portable computers or lap top computers where space constraints increase the need for system resource optimization. The design and use of hardware devices under the PCMCIA standard are well known in the art. It will be apparent to those skilled in the art that other implementations of removable system resources are possible.
Virtually all computer systems operate with some sort of operating system or software processing logic. The use of an operating system in a computer system is well-known in the art. The operating system is responsible for managing the processing and transfer of information between various system resources. One well known technique for managing these resources is the use of device drivers. Device drivers are software modules comprising processing logic for controlling the low level or device specific components of a particular computer system resource. For example, a device driver may be used for controlling a magnetic disk drive device coupled to a computer system. In this example, the device driver would control the various hardware specific registers, latches, signals, or other components of the magnetic disk drive device. Similarly, other computer system resources such as serial or parallel input/output (I/O) ports, modem devices, computer network interface devices, or memory expansion boards are controlled by device drivers.
In conventional computer systems, device drivers are typically loaded into random access memory (RAM) during bootstrap initialization of the computer system. Many prior art computer systems require that device drivers be loaded at initialization time in order for random access memory to be allocated properly. Depending upon the complexity of the device controlled by the device driver, the device driver itself may be relatively small or a very large device driver that consumes many thousands of bytes of random access memory. Thus, many prior art systems require that a full system configuration of resources be installed and available at bootstrap initialization time. If system resources or interfaces are subsequently added or removed from the system, the inability to access a newly installed resource or the errant access to a now unavailable system resource usually results. Other prior art computer systems require that the computer system be powered down while new system resources or features are added or removed from the system. Still other systems must at least be newly bootstrap loaded in order to gain access to a new configuration of system resources. Thus, prior art computer systems cannot be readily reconfigured to a new arrangement of system resources.
Because prior art systems typically require that a full system configuration of resources be established at initialization time, the tendency exists for any or all system resources that may conceivably be used while a computer system is powered up to be installed during the initialization process. This tendency leads to the installation of resources that are never used during a computing session. The loading and installation of unused system resources increases the time required for bootstrap initializing the system and reduces the available random access memory (RAM), because of the RAM space required by unused device drivers. It is, therefore, important to install in a computer system only those device drivers actually needed during a computing session. In some cases, it may not be possible to load all of the device drivers necessary because of the random access memory storage constraints.
Some computer systems in the prior art provide means for interfacing with removable electronic feature cards. In order to mitigate the disadvantages described above, some of these computer systems store associated device drivers on the removable electronic feature card itself. In this way, random access memory space within the computer system does not need to be allocated for storage of the device driver. Moreover, processing time during initialization is not consumed by having to load the device driver into random access memory. Systems that configure device drivers on the removable feature cards have the advantage of optimizing memory allocation requirements within the computer system.
Systems that configure device drivers on removable feature cards, however, have several important disadvantages. First, if a feature card is removed from the computer system, the device driver controlling the operation of the feature card becomes inaccessible to the computer system. In most cases, the computer system requires access to a device driver in order to properly terminate the operation of the device prior to removal of the feature card. Typically, the computer system does not have sufficient time to access the device driver prior to removal of the feature card. Thus, system errors often result from an improperly terminated system resource.
Other computer systems having means for interfacing with removable electronic feature cards provide a very limited capability for responding to insertion or removal of feature cards during post initialization operation of the computer system. Some computer systems do not recognize system resources connected to the computer system after the bootstrap initialization process has been completed. Other computer systems suspend or freeze the operation of the computer system if a system resource is removed after initialization is complete. Still other computer systems require that the system be powered down or the bootstrap initialization process be reinitiated if a new configuration of system resources is desired.
This application is a continuation-in-part of U.S. patent application Ser. No. 07/815,331, filed Dec. 27, 1991, and entitled "Device Driver Configuration In a Computer System". The disclosure of the parent application, Ser. No. 07/815,331, described a computer system having dynamic device driver configuration for removable system resources. In the computer system of the parent application, a feature card device driver is stored in a memory area of the card. The device driver is separated into two parts: 1) a full device driver portion, and 2) a stub device driver portion. The full device driver provides all of the device driver functionality necessary to control each and every function of the feature card. The device driver stub is a small compact portion of processing logic associated with the full device driver, but mainly responsible for linking the full device driver with operating system software located in the computer system.
Upon insertion of a card into the computer system, the device driver stub code image is read from the card memory area and transferred into an area of computer system memory. The device driver stub code is then executed by the processor of the computer system from computer system random access memory. Conversely, the full device driver code is not transferred to the computer system random access memory; rather, the full device driver is executed while still resident on the card. Upon execution, the device driver stub enables access to the full card resident device driver and allows memory mapping to the full device driver. The full device driver may then be activated by the processor.
When a card is removed from the computer system, the device driver stub disables access to the removed card by disallowing memory mapping to the removed card. The card insertion flag is reset to indicate that the removable system resource has been decoupled from the computer system and the device driver stub is unlinked from the linked list of active device driver stubs.
However, in the invention of the parent application, each device driver stub loaded into computer system memory remains resident in the computer system memory until the next time the system is bootstrap initialized. Therefore, while the invention of the parent application permits dynamic device driver configuration for removable computer system resources, the fact that the computer system has a finite amount of system memory places an upper limit upon the number of removable resources that can be used by the system before the system must be reset with a bootstrap initialization operation. The requirement that a system be reset is an undesirable feature because a system cannot be used while a bootstrap initialization is being performed. Furthermore, a bootstrap initialization operation destroys the contents of computer system memory. Therefore, any data residing in main memory will be lost if it had not been saved prior to the bootstrap operation.
Thus, a better means for dynamically configuring system resources in a computer system is needed.